The invention relates to an arrangement for determining the mass of a narrow, more or less enclosed stream of tobacco, filter rod material, or other constituent material of smoker's products, and the like, using a measuring capacitor having electrodes connected to a high-frequency voltage source, with a measuring capacitor constituting at least part of the frequency-determining reactance of a circuit operative for generating a high-frequency periodic signal, preferably a variable-frequency resonant circuit.
A stream of tobacco or other material is to be considered "enclosed", for the purposes of the present description, if conveyed in a certain manner. The enclosing can be, for example, that constituted by provision of a wrapper, such as a wrapper made of paper (cigarette paper) or tobacco strips. However, the enclosing can also be constituted by the provision of boundary walls in a guide conduit for tobacco or other material, such walls being either stationary or travelling with the material.
Capacitive methods for measuring the density of a continuous cigarette rod in a cigarette rod forming machine are known, for example, from U.S. Pat. No. 2,357,860. The electrodes of the measuring capacitor are connected to the terminals of a high-frequency voltage source and are configurated as plates arranged on opposite sides of the continuous cigarette rod. The capacitor constituted by the electrodes, between which the cigarette rod travels, forms part of a high-frequency resonant circuit which, in response to a change of the tobacco mass in the continuous cigarette rod, undergoes detuning, such detuning constituting a direction indication of tobacco mass variation.
However, in actual practice, the prior-art capacitive measuring arrangements produce output signals which are incapable of being reliably processed for the purpose of making a determination of the tobacco density. As a result, the art has turned more and more to nuclear measuring expedients according to which the wrapped continuous cigarette rod is penetrated by beta rays emitted from a radioactive substance, such as strontium-90, with the weakening of the emitted radiation which results from passage of such radiation through the material of the cigarette rod being determined by means of an ionization chamber.
The use of radioactive materials in the foodstuffs industry, to which in a broad sense the tobacco-processing industry belongs, is subject to stringent governmental regulation in all countries. In order to generate highly responsive measuring signals -- i.e., signals which change in value in almost immediate response to changes in the irradiated material and thereby accurately indicate mass variations along even a small length of a stream of such material -- it is necessary to use an undesirably high radiation power.
Finally, for reasons involving the structure of the nuclear measuring devices, it is very difficult to measure the density of a continuous tobacco rod at a location upstream of where it is wrapped in a cigarette paper, or the like. However, measurement at just such location is particularly important, because it makes possible a correction of for example the mass excess of a stream portion before such portion reaches the wrapping location. Such correction usually involves the removal of excess tobacco or other material from the travelling stream in a controlled manner resulting in a stream of relatively uniform mass in the region of the wrapping location.
From the foregoing it follows that a capacitive measuring method, at least for the generation of signals for determining the short-lasting fluctuations in the mass of the tobacco stream or rod, would be extremely advantageous, if it made possible the generation of usuable signals.